1. Field of the Invention
The present invention relates to Ni-based superalloys excellent in strength, hot corrosion resistance, and oxidation resistance each at high temperature. It also relates to parts or components, such as gas turbine blades, using the Ni-based superalloys.
2. Description of Related Art
In engines such as jet engines and gas turbines, turbine inlet temperature is being elevated higher and higher so as to increase performance and efficiency of the engines. Materials for use in turbine blades that should endure such elevated temperature are required to have excellent creep rupture strength and high toughness as to endure centrifugal force at high temperature, as well as excellent oxidation resistance and corrosion resistance to high-temperature combustion gas atmospheres. Ni-based alloys are presently used to satisfy these requirements. Ni-based alloys are roughly classified as conventional casting alloys containing equiaxis grains; uni-directional solidification alloys containing columnar grains; and single crystal alloys each containing a single crystal grain.
Conventional cast Ni-based alloys having high Cr contents are used in land based gas turbines (gas turbines that are fixed on the ground and used for power generation) using fuels containing large amounts of impurities in consideration of their hot corrosion resistance and cost. Exemplary alloys that are oriented to satisfactory corrosion resistance include conventional casting alloys disclosed typically in Document 1 (Japanese Patent Laid-open No. Sho 51-34819), Document 2 (Japanese Patent Laid-open No. 2004-197131), and Document 3 (U.S. Pat. No. 3,459,545). Concerning conventional casting alloys for use in land based gas turbines, there are alloys having higher strength while sacrificing their hot corrosion resistance, such as alloys disclosed in Document 4 (Japanese Examined Patent Publication No. Sho 46-27144) and Document 5 (Japanese Patent Laid-open No. Hei 06-57359).
The conventional casting alloys for use in the gas turbines are required to have further improved strength because they have lower strength than the uni-directional solidification alloys and the single crystal alloys.
The uni-directional solidification alloys and the single crystal alloys are mainly used in the jet engine blades and nozzles (vanes). Such alloys for use in the jet engine blades and the nozzles are oriented to higher strength and have higher creep rupture strength by containing Cr in a smaller content and containing large amounts of tungsten (W) and tantalum (Ta) that effectively contribute to solution hardening. The resulting alloys, however, are not suitable for land based gas turbines using fuels containing large amounts of impurities, because they are insufficient in hot corrosion resistance although they have high creep rupture strength. Additionally, these alloys show low casting yields because they require complicated casting processes.
Accordingly, an object of the present invention is to provide a Ni-based conventional casting alloy that excels in corrosion resistance and oxidation resistance and has high strength.